Field of the Invention and Description of the Related Art
The present invention relates to an electronic endoscope system equipped with a color smear reducing means for reducing or suppressing a degree of color smear.
Recently, there have widely been used endoscopes of which long and narrow insert portions can be each inserted into a living body or the like for observing an object such as the diseased part.
Meanwhile, electronic endoscopes have lately been put into practice using solid imaging devices, e.g., CCD's, as imaging means.
Known as one of such electronic endoscopes is a frame sequential type that an object is illuminated by beams of illumination light different in wavelength from one another, such as red, green and blue beams, and images picked up under illumination of light beams of respective wavelengths, i.e., component images, are synthesized to produce a color picture.
With the above type electronic endoscope, component images taken at different time points are synthesized to produce one frame of color picture. Therefore, the synthesized color picture tends to cause color smear, if the object is moving or if there is a relative movement between an imaging means and the object.
As one prior art aiming at prevention of such color smear, Japanese Patent Laid-Open No. 61-71790 has proposed to detect a movement of an object and change an imaging speed dependent on the detected movement speed, thereby preventing the occurrence of color smear.
In order to change the imaging speed, the above prior art makes control for varying a rotational speed of a rotatable color film which constitutes a frame sequentially illuminating means. However, the rotational speed of the rotatable color filter is generally quite low in response to its change. This makes it difficult to follow the movement of the object.
Accordingly, the above prior art is disadvantageous in that the control is less adaptable for the object which develops a movement in a very short time, or changes an amount of movement over time, for example.
Another prior art of Japanese Patent Laid-Open No. 61-71791 has disclosed an endoscope apparatus which comprises an imaging means of the frame sequential type, a color smear detecting means for detecting color smear of a picture based on a difference between images picked up by the imaging means at different time points, and a color smear correcting means for making color smear correction on a still picture or freeze-picture, which is output from the imaging means and undergoes color smear, by allowing a user to specify the direction and value of the color smear, when the presence of color smear is determined by the color smear detecting means.
The above prior art is problematic in that when color smear is detected, the user must input correction values to eliminate the color smear and hence the disclosed apparatus cannot be adapted for a motion picture. The prior art endoscope apparatus cannot also reduce the color smear in real time.
Furthermore, the prior art of Japanese Patent Laid-Open No. 63-276676 discloses a corresponding area detection device for detecting corresponding areas in plural images by the use of an arithmetic means for correlation. Owing to use of the arithmetic means for correlation, this prior art is difficult to determine the corresponding areas in real time. Therefore, the disclosed device has also a problem that it cannot be adapted for a motion picture.
If the above prior art is employed to reduce color smear, the device necessary for reducing color smear would be large in scale and the cost would be increased.